Grinding apparatus with infeed control

ABSTRACT

A grinding apparatus comprising abrasive disc means including at least one abrasive disc, means for mounting the abrasive disc means for rotative displacement about the axis of the abrasive disc means, means for rotationally displacing the abrasive disc means, means for axially displacing the abrasive disc means towards a workpiece surface to be ground, means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of the disc, means for repetitively displacing the mounting means through a first zone wherein only a portion of the workpiece surface overlaps the abrasive disc and through a second zone wherein the abrasive disc completely overlaps the workpiece surface, and means for activating the axially displacing means only when the mounting means is located within the second zone.

United States Patent [191 1 3,812,624

Dunn May 28, 1974 l GRINDING APPARATUS WITH INFEEI) Primary Examiner--0thcll M. Simpson CONTROL Assistant Examiner--Nicholas P. Godici t t Attorney, Agent, or Firm-Spencer T. Smith [75] Inventor: Elman R. Dunn, Roscoe, Ill.

[73] Assignee: Litton Industries, Inc., Beverly Hills, [57] ABSTRACT Calif. g A grinding apparatus comprising abrasive disc means [22] Filed; A i including at least one abrasive disc, means for mountmg the abraslve (1180 means for rotative displacement PP 306,309 about the axis of the abrasive disc means, means for rotationally displacing the abrasive disc means, means wwwvmw for axially displacing the abrasive disc means towards U-S- Cl- 5 a workpie e urface to be ground means for mounting [5 r a workpiece having at least one surface to be ground [58] Field of Search 51/1 11 R, H2, H5, 113, by the abrading action f the f f the disc, means 51/114, 215 CP, 234, 1659 for repetitively displacing the mounting means H through a first zone wherein only a portion of the V V v I workpiece surface overlaps the abrasive disc and [56] References cued through a second zone wherein the abrasive disc com- UNITED STATES PATENTS pletely overlaps the workpiece surface, and means for 1,966,194 7/1934 Yager 5l/115 activating the axially displacing means only when the 2,123,705 7/1938 Ball 5l/l22 mounting means is located within the Second zone. 3,382,622 5/1968 Dunn 51/1 15 5 Claims, 4 Drawing Figures PATENTEDMAY28 I914 3,812,624

SHEEI 2 0F 2 1 GRINDING APPARATUS WITH INFEED CONTROL This invention relates to horizontal double disc grinders for grinding opposed faces of a workpiece to within stringent tolerance limits for flatness and parallelism.

In conventional facecut grinding a feed mechanism axially advances either one or two abrasive discs continously and at a uniform infeed rate while a workpiece is repetitively displaced across the cutting face(s) of the abrasive disc(s).

A workpiece which is either linearly reciprocated across the abrasive discs by gun-type fixturing or rotatively oscillated along an arcuate path by an oscillating arm must be displaced at least partially into the central bore area of the abrasive disc (partially beyond the inner perimeter) where the abrasive discs include a central bore and at least partially beyond the outer perimeter of the abrasive discs to prevent .shoulderlike plateaus from being generated adjacent the inner and outer peripheries of the abrasive discs. When the surfaces of the workpiece being ground only partially overlap the abrasive discs the grinding pressure exerted by the abrasive discs against the workpiece increases since the infeed rate is constant whereas the workpiece area being subjected to the infeed force is reduced. This grinding pressure accordingly varies inversely with the extent of overlapping. Excessive abrasive wear therefore results at the inner and outer perimeters of the discs and frequent dressing operations are required to restore the faces of the abrasive discs to their original shape. This results in the loss of time and excessive abrasive disc wear.

Attempts have been made to correct this problem by designing abrasive discs which have harder abrasive grains in the outer peripheral zone than in the intermediate or central peripheral zone and by designing abrasive discs wherein the abrasive bond is varied so that abrasive grains will be more readily released at the central portion of the discs. These abrasive discs are substantially more expensive than conventional abrasive discs and do not yield completely satisfactory results.

It is, therefor, an object of the present invention to provide a grinding apparatus of the type described, wherein a substantially flat wear pattern will be achieved across the abrading faces of the abrasive discs.

Among the advantages of the present invention is the provision of a grinding machine which may successfully utilize abrasive discs having a uniform abrasive character.

Other objects and advantages of the present inven tion will become apparent from the following portion of this specification and from the accompanying drawings which illustrate in accordance with the mandate of the patent statutes a. presently preferred embodiment incorporating the principles of the invention.

Referring to the drawings:

FIG. 1 is a front perspective view of a horizontal double disc grinder constructed in accordance with the teachings of the present invention;

FIG. 2 is a plan view illustrating the double disc grinder illustrated in FIG. 1;

FIG. 3 is an enlarged elevational view of a portion of the grinding apparatus of the present invention;

FIG. 4 is a schematic diagram showing the hydraulic controls of the present invention.

The basic components of a horizontal double disc grinder 10 are illustrated in FIG. 1. The double disc grinder includes left and right hand abrasive discs 12, 12, which preferably have central axially extending bores 14, 14' therein (FIG. 3) and which preferably have uniform abrasive characteristics across the parallel abrading faces thereof. These discs are conventionally rotatably mounted on a pair of slides l6, 16' which are longitudinally displaceable for facecut infeed along a machine bed 18. Conventional feed mechanisms 20, 20' such as are disclosed in U.S. Pat. Nos. 3,513,600, granted May 26, 1970 and US. Pat. No. 3,001,337, granted Sept. 26, 1961 which are actuated by motors 22, 22' selectively advance these abrasive discs 12, 12' in unison towards the workpiece W at a selected facecut infeed rate to control stock removal from the parallel faces 24, 24' (FIG. 2) of the workpiece W. The workpiece may either be a single unit wherein either a single or two opposing faces are to be ground or a pair of units wherein only a single surface of each unit will be ground.

The horizontal double disc grinder 10 has an arm 26, which is pivotably mounted on a rock shaft 28. The rock shaft 28 is. journaled in bearings (not shown) which are housed by support brackets 30, 30' secured to the front of the bed 18. A work holding paddle 32, including an opening 34 for receiving a retaining frame 36 for securely holding a workpiece W in a predetermined position, is secured to the arm 26.

The arm 26 is selectively displaceable from a fully retracted position P, whereat the workpiece can be conveniently secured within the workframe 36 to an intermediate partially advanced P, position wherat the surfaces of the workpiece W which are to be ground only partially overlap the abrading faces of the abrasive discs proximate the outer periphery 40 thereof and then to a fully advanced position P whereat the surfaces of the workpiece W which are to be ground only partially overlap the abrading faces of the abrasive discs at the inner periphery 42 thereof (FIG. 3).

A hydraulic motor 46, which is secured to a bridge plate 48 through an intermediate trunnion pin 50 and a bracket 52 includes a piston rod 44 (FIG. 3) which is connected to the arm 26 by a clevis bracket 62. Reciprocation of piston rod 44 oscillates the arm 26 along an arcuate path between the fully retractedposition P, and the fully advanced P position.

After the workpiece has been mounted within the retaining frame th arm is rotatively displaced to the partially advanced (partially retracted) position P, and is then repetitively oscillated between positions P, and P until the workpiece-surfaces are completely ground. The arm will then be returned to the fully'retracted position P, to complete the cycle.

The workpiece and more particularly the surfaces of the workpiece which are to be ground are thereby repetitively and sequentially oscillated through a first zone wherein these workpiece surfaces only partially overlap the abrading faces of the grinding discs proximate the outer periphery thereof, through a second zone wherein the workpiece surfaces and the faces of the abrasive discs completely overlap and finally through a third zone wherein the workpiece surfaces only partially overlap the abrading faces of the grinding discs proximate the inner periphery thereof.

Facecut infeed of the abrasive discs is halted whenever the workpiece surfaces are located within the first which carries a cam 74 is mounted on the second switch plate 66. This cam 74 includes sloping surfaces 76, 78 adjacent a central level portion 80.

A guard plate 82 is secured to the bridge plate 48 for directing the flow of coolant spray intoa drainage tank 84 and a portion 86 of the guard plate 82 forms a bracket on which first and second limit switches 88, 90'

are mounted. Operating lever 92 of the second limit switch 90 is selectively positioned to engage camming surfaces 76, 78, 80 only when the surfaces of the workpiece which are to be ground fully overlap the abrading faces of the grinding discs whereby the infeed mechanisms 22, 22' (FIG. 3) will only be actuated while the workpiece surfaces are located within this second zone. Operating lever 94 of the first limit switch 88 is selectively positioned to engage the first trip dog 68 when the arm 26 is partially retracted to position P, and is selectively positioned to engage the second trip dog 70 when the arm 26 is fully advanced to position P The hydraulic system for controlling the oscillation of the arm 26 is disclosed in FIG. 4; This system includes a first two position valve 100 which is controlled by a solenoid 102. Whenthe solenoid102 is in the unenergized state, spring 104 maintains the valve 100 in a first position, and when the solenoid is first energized through manual pushbutton control (not shown) the valve 100 is displaced against the action 'of the spring 104 to a second position which'causes paddle 32 toadvance to position P and reverse. The system additionally includes a two position double channel valve 106 (shown in its first position), a plunger deceleration valve 108, and the fluid cylinder or motor 46.

When the operating lever 94, during retraction mothrough lines 118 and 126 to the rod 44 end of the cylinder 46. The circuit now functions to permit the passage of fluid from the head end of the cylinder through lines 120 and 127 into a fluid reservoir 128. The piston is accordingly displaced towards the left and the arm 26 is rotated in the counter clockwise direction. Throttle valves 130, 130' are provided to control the rate at which the pressurized fluid is directed to the cylinder.

In order than the grinding surfaces which are passing past the workpiece surfaces will wear uniformly, the rotational velocity of the oscillating arm, when the work piece surfaces are being displaced through zone two, should vary with its angular position and the ratio of the rotational velocity of the arm 26 when the workpiece W is at P, to the velocity of the arm 26 when the workpiece W is at P should approximately be equal to (2R w/ (2R +w) where w is the width of workpiece W and the rotational velocity of the arm 26 should vary substantially linearly therebetween.

The plunger or deceleration valve 108 includes a plunger element 132 which is selectively displaceable from a retracted position to an advanced position. As this valving plunger 132 is advanced, the pressure drop through the valve is increased whereby the pressure acting on the cylinder will be reduced.

A cam support rail 140 is secured at one end to the oscilitable arm 26 and a pin element 142 which is secured to the housing is located within a slot 144 defined tion of paddle 32, strikes the first trip dog 68 at position P the solenoid 102 is actuated. Fluid under, pressure is directed from a source 110 through fluid lines 112, 114 to the two position valve which has been shifted to its second position. The pressurized fluid is passed through the valve to fluidline 116 to the second valve 106 for urging the displacement of this valve to its second position whereby a circuit will be defined therethrough by fluid lines 118, 120 into .the headend of cylinder 46. Additional pressurized fluid from the source will be directed through lines 112, 122, through I the plunger valve 108 and lines 118, 126, and into the rod end of fluid cylinder 46 Piston 124', due to differential areas being pressurized alike, is accordingly displaced to the right thereby rotating arm 26 in the clockwise direction (FIG. 3).

When the operating lever 94 again strikes the second trip dog 70 at the fully advanced position P,,, the solenoid is deenergized and the two position valve is dis placed by spring 104 to the first position whereby the pressurized fluid will be directed from the source through lines 112 and 114, valve 100, and line 124 to the second valve 106. This valve is displaced to its first position whereby a circuit is defined therethrough by lines and 127; Pressuirzed ,fluid'is also'directed through lines 112, 122, through plunger valve 108,

in the other end of the cam support rail which extends in a direction parallel to the piston rod.

This cam support rail 140 includes awedge-shaped element 148 having a substantially linear camming surface selectively inclined so that as the workpiece is displaced from P1 to P,,, the plunger element will be advanced from its retracted to its advanced position which are predetermined so as to produce piston velocity, of piston 124, at these two extreme'locations having the above defined ratio and to produce piston velocity, and hence arm 26 velocity which varies substantially linearly therebetween.

The arm 23 ,will be fully retracted when a predetermined number of oscillations are completed and the limit switch 152 will be closed to complete the grinding cycle for a single workpiece W. The right hand and left hand abrasive discs 11 and 12 may be rapidly retracted by feed means 22, 22 either when the counters (not shown) time out, or when the limit switch 152 is closed.

The principles of the present invention are applicable to single as well as double disk grinders and is applica abrasive disc means including atleast one abrasive disc havinga central axially extending bore, means for, mounting said abrasive disc for rotative displacement about the axis of said abrasive disc,

means for rotationally displacing said'abrasive disc,

means for axiallydisplacing said abrasive disc towards a workpiece surface to be ground,

means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of said abrasive disc,

means for displacing said mounting means from a first zone wherein only a portion of the workpiece surface overlaps said abrasive disc, through a second zone wherein said abrasive disc completely overlaps the workpiece surface to a third zone wherein a portion of the workpiece surface lies within the abrasive disc bore, and

means for activating said axially displacing means only when said mounting means is located within said second zone.

2. A grinding apparatus according to claim 1, wherein said abrasive disc means comprises a pair of coaxial discs and said mounting means displacing means selectively displaces said mounting means intermediate said discs.

3. A grinding apparatus according to claim 1, wherein said mounting means includes an arm member and means for supporting said arm member for pivotal displacement.

4. A grinding apparatus according to claim 1, wherein said mounting means displacing means further comprises means for displacing said mounting means sequentially through said second and first zones precedent to displacing said mounting means sequentially through said first and second zones.

5. A grinding apparatus according to claim 1, wherein said mounting means displacing means further comprises means for displacing said mounting means sequentially through said third, second and first zones precedent to displacing said mounting means sequentially through said first, second and third zones. 

1. A grinding apparatus comprising abrasive disc means including at least one abrasive disc having a central axially extending bore, means for mounting said abrasive disc for rotative displacement about the axis of said abrasive disc, means for rotationally displacing said abrasive disc, means for axially displacing said abrasive disc towards a workpiece surface to be ground, means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of said abrasive disc, means for displacing said mounting means from a first zone wherein only a portion of the workpiece surface overlaps said abrasive disc, through a second zone wherein said abrasive disc completely overlaps the workpiece surface to a third zone wherein a portion of the workpiece surface lies within the abrasive disc bore, and means for activating said axially displacing means only when said mounting means is located within said second zone.
 2. A grinding apparatus according to claim 1, wherein said abrasive disc Means comprises a pair of coaxial discs and said mounting means displacing means selectively displaces said mounting means intermediate said discs.
 3. A grinding apparatus according to claim 1, wherein said mounting means includes an arm member and means for supporting said arm member for pivotal displacement.
 4. A grinding apparatus according to claim 1, wherein said mounting means displacing means further comprises means for displacing said mounting means sequentially through said second and first zones precedent to displacing said mounting means sequentially through said first and second zones.
 5. A grinding apparatus according to claim 1, wherein said mounting means displacing means further comprises means for displacing said mounting means sequentially through said third, second and first zones precedent to displacing said mounting means sequentially through said first, second and third zones. 